I don't worry much about it.
There's too many things that hit the edges of any defenition.
Like the Piedmont stamps. Paper? yep, Baseball image? yep, issued as enticement to buy a product? yep. Card????? Nope, maybe,
Postcard back exhibits? Paper, baseball, issued to collect OR send. They're cards, but also postcards, so the defenition seems to include some postcards, but not others.
Donruss puzzles? paper, baseball, oops, they were technically the product that the cards were the enticement to buy at first, then became the enticement to buy the cards, then became junk sort of. Cards???
Cards or not I'll collect them.
Steve B